Like many good solutions in programming, you achieve this by adding a layer of indirection. Specifically, what we can do here is add a table between action tags (i.e. “Example” and “Another”) and their respective payloads. type ActionPayloadTable = { “Example”: { example: true }, “Another”: { another: true }, } then what we can … Read more
You’re mostly on your own. A note in the standard explains this (9.5/2): If any non-static data member of a union has a non-trivial default constructor (12.1), copy constructor (12.8), move constructor (12.8), copy assignment operator (12.8), move assignment operator (12.8), or destructor (12.4), the corresponding member function of the union must be user-provided or … Read more
The problem is that the compiler doesn’t know how to do narrowing on an object property like IceCreams[item] where you are indexing with a key whose type isn’t known to be a specific literal type. TypeScript is only following the type of the index, not the identity. And the type of item is string. If … Read more
I don’t really like the type-checking and type-casting solutions provided above, so here’s 100% type-safe union which will throw compilation errors if you attempt to use the wrong datatype: using System; namespace Juliet { class Program { static void Main(string[] args) { Union3<int, char, string>[] unions = new Union3<int,char,string>[] { new Union3<int, char, string>.Case1(5), new … Read more
This is an issue with the way excess property checks work on unions. If an object literal is assigned to a variable of union type, a property will not be marked as excess if it is present on any of the union members. If we don’t consider excess properties to be an error (and except … Read more